It may be a reference to guitar amp tubes, which can have different distortion sounds. Hence "this one sounds fatter or richer" (EL34's), vs. "this one sounds more glassy" (6550's apparently). Of course, other circuits in the guitar amp would make a difference also. But I"ve seen similar comments about tubes on guitar forums, so that may be where the terminology is coming from -- or where it is aimed at.

I once rebuilt a PAS 3 preamp with metal film resistors and polyprop caps, as I had easy free access to the parts to do it. Then I did run that preamp in my system awhile but with a solid state power amp. I tried swapping Mullard and Telefunken tubes back and forth, and yes, I could hear some difference between the brands. But that was the 80s when my hearing was better and those kind of tubes were not like gold coins.

I once rebuilt a PAS 3 preamp with metal film resistors and polyprop caps, as I had easy free access to the parts to do it. Then I did run that preamp in my system awhile but with a solid state power amp. I tried swapping Mullard and Telefunken tubes back and forth, and yes, I could hear some difference between the brands. But that was the 80s when my hearing was better and those kind of tubes were not like gold coins.

If you can remember the 80s, you weren't there..

_________________deVE7ASO VE7ZSOAmateur Radio Literacy Club. May we help you read better.Steve Dowve7aso@rac.ca

In guitar lingo, fatter is more overdrive, more distortion. Sounds like Purple Haze. The easy way to achieve fat-ness is with a pedal or Fuzz box type effect ahead of the amp. Basically a preamp. Randy Bachman did this years ago by plugging one amp into another. Then his amp guy built him a proper preamp they call the Herzog for some reason. Listen to the lead of American Women, or No Time Left for You.

What are they talking about fat output tubes? Probably, that tube starts to distort earlier than the others, so takes less overdrive to reach that level where the output waveform is flattening if you watched it on a scope.

Fat is ugly in the world of HiFi, so steer clear of that stuff.

In a HiFi amp, you will never hear the difference, because you wouldn't dream of operating the tube outside of its designed specs.

Fatter tone to me means the tube is different than the original spec for the tube number hence the different sound and should have its own tube number, because if it were the same exact tube it would have the same sound as all other tubes of that type.

An example.

I do know that a new manufacture 12AT7 will not work as the FM oscillator in some German radios. Simply does not oscillate. So to me it should have its own tube number because it's obviously not a 12AT7 if it don't work in a circuit designed for a 12AT7.

On a more serious note, I ran into a really cool video demonstrating a 6BN6 used as a guitar distortion effect. The video had a bass guitar plugged into the circuit, and the sound had the heavy "squarewave" clipping like that heard on "American Woman." The one thing missing from the video that I wish had been included would have been an oscilloscope showing the output waveforms.

The only parameters that I could imagine a tube manufacturer improving upon while still claiming that their tube is the same as one with an identical part number are the mean time between failures or the amount of heat radiated from the bulb. If a manufacturer claimed, for instance, to make an "improved 6L6," and the improvements were achieved by building a tube with characteristic curves were different than those published by the company that first made 6L6s in the 1930s, then this new tube wouldn't be a 6L6. It would be something different.

They should number the improved tubes like they did way back when how they kept the basic tube number, but added letters after the number to signify it was still the same basic tube only improved characteristics and that it could usually sub for the original tube.

Now if the tube characteristics are changed such that the tube is nothing like the original tube then it should have a new number.

Fatter tone to me means the tube is different than the original spec for the tube number hence the different sound and should have its own tube number, because if it were the same exact tube it would have the same sound as all other tubes of that type.

An example.

I do know that a new manufacture 12AT7 will not work as the FM oscillator in some German radios. Simply does not oscillate. So to me it should have its own tube number because it's obviously not a 12AT7 if it don't work in a circuit designed for a 12AT7.

Which German radio uses a 12AT7 in the oscillator? Every one I've ever seen uses either a 6AQ8 or a pair of 6AB4's.